1. Field of the Invention
The invention relates to method and apparatus for achieving increased hydrocarbon recovery by enlarging the effective recovery zone along a generally horizontal axis relative to the primary borehole. The apparatus consists of a flexible drill shaft and downhole assembly for controlling position and direction of lateral hole formation relative to producing hydrocarbon zones. The particular flexible shaft may find diverse utility in the related geophysical and mining fields.
2. Description of the Prior Art
The prior art has included a number of attempts at horizontal drilling wherein assemblies function from a primary borehole in an attempt to drill laterally therefrom. Such prior attempts have been marginally successful at best since no reliable, ongoing practice has evolved while the benefits to be derived are fairly evident. A U.S. Pat. No. 2,198,016 in the name of Rogers et al provides a teaching that utilizes a combination of a helical coil contained within a wire sheath and functioning within a series of stabilizing rings. This teaching utilizes but a single coil shaft portion and must rely on sheathing and encircling stablizing rings for further reliability in producing hole.
U.S. Pat. No. 2,441,881 in the name of Hays also attempted construction of a horizontal drill shaft using a linear series of coil springs as stabilized internally by down-flowing fluid pressure. The following patents also each disclosed a combination of force transmission elements adapted for deviation or lateral direction drilling from a generally vertical borehole:
Granville, U.S. Pat. No. 1,367,042 PA1 Prindle, U.S. Pat. No. 1,595,922 PA1 McCune, U.S. Pat. No. 2,726,847 PA1 Bull, U.S. Pat. No. 3,958,649
Each of the above patents relates to some form of hybrid-type linkage device in a serial connection that may be rotationally driven and controllably positioned for lateral directional drilling procedure. The patent to Granville discloses yet another coil spring combination wherein a helically wound, tightly coiled element is operated in combination with a central chain linkage that is universally interconnected between opposite ends of the drill shaft. None of the prior art discloses the use of a combination of oppositely wound coil shafts that are maintained in flush disposition both radially and along the length of the drill shaft thereby to provide reliable, straight drive rotational force once redirected.